A hybrid vehicle may include an engine and a motor for propelling the vehicle. The engine may be stopped and not rotating when driver demand torque may be met via the motor. Stopping the engine may conserve fuel and reduce vehicle emissions. However, if a human driver requests a large increase in driveline torque output, the engine may have to be restarted to meet the driver demand torque. The driver may notice that maximum driveline torque is not available until after the engine starts and achieves a speed of the driveline. The engine may take more than one or two seconds to start and achieve a speed where it may contribute torque to the driveline. Consequently, the driver and vehicle passengers may notice a delay in torque provided to the driveline. The delay in torque production may be objectionable.
The inventor herein has recognized the above-mentioned issues and has developed a driveline operating method, comprising: ceasing fuel delivery to all engine cylinders and adjusting an actual total number of cylinders of an engine with operating poppet valves and an actual total number of cylinders of the engine with deactivated poppet valves in response to a desired driveline braking torque during vehicle deceleration via a controller.
By operating different engine cylinders in different valve modes while fuel is not injected to an engine during vehicle deceleration, it may be possible to provide driveline braking while improving a driveline's capability to provide torque in response to a request to increase engine torque after combustion in engine cylinders ceases. For example, if a small amount of driveline braking is requested and an electric machine has capacity to provide the desired driveline braking, an engine may be rotated with valves held closed to reduce engine pumping losses. Keeping the engine rotating may reduce engine starting time by not having to accelerate the engine from zero speed to a speed of the driveline before torque may be provided by the engine to the driveline. If a larger amount of driveline brake torque is requested, engine cylinders may be operated with valves that open and close so that the desired driveline braking may be provided by the engine and the electric machine while still not injecting fuel to the engine.
The present description may provide several advantages. For example, the approach may reduce engine starting time. Further, the approach may reduce driveline response time to a request to increase driveline torque. Additionally, the approach may improve vehicle fuel economy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.